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  • 1.
    Hatem, Mohammed
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Cement-Poor Concrete and Grout for Use in Underground Constructions2014Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    This thesis deals with the composition and properties of cement-based materials, concrete and grout, for use as seals and for stabilizing fracture zones in underground facilities like mines and repositories for chemical and radioactive waste. It is of general character with respect to the composition and preparation of concretes and grouts but focuses on the sealing of boreholes for mineral prospection and site investigation for locating underground repositories of hazardous waste.The proposed principle of constructing concrete seals in very deep boreholes (VDH) where they are intersected by fracture zones is to cast the concrete on-site over placed clay seals to the upper end of the respective fracture zones where the next clay seal is installed. The chemical interaction between concrete and clay causes mutual degradation that must be taken into consideration. Ordinary concrete with Portland cement as binder is not suitable because of its poor chemical stability over long periods of time and because of its high pH, more than 12, which attacks contacting clay seals. Another drawback is that such concrete requires organic superplasticizers for achieving fluidity and they can give off organic colloids that can transport radionuclides. Inorganic fluidizers like talc and use of low-pH cement offer new possibilities to prepare suitable concretes and grouts. They are the focus of this present document.The criteria for the concrete seals are: sufficient fluidity and coherence at casting and sufficiently high bearing capacity and low compressibility for maintaining constant volume conditions under the load of the overlying series of clay and concrete. The hydraulic conductivity of the hardened concrete should be lower than that of the surrounding fracture zone.Since the concrete must perform acceptably for up to 100,000 years and the cement component will ultimately be dissolved and lost, the rest, i.e. the aggregate components, must still provide acceptable support for overlying clay and concrete seals in deep boreholes. The aggregate component must therefore be very densely packed and have a granular composition that resists erosion.The main objectives of this study are: 1) To investigate the performance of new types of cement-poor, organic-free concrete for long-term duty under normal and extreme hydrothermal conditions at varying temperatures. Properties of special importance are fluidity, mechanical strength, rate of strengthening, pH, and minimum impact on contacting seals of smectite-rich clay seals.2) To investigate the function of new cement-based grouts proposed for sealing finely fractured rock around boreholes, tunnels and shafts where concrete seals will be cast, especially with respect to fluidity, rheological behaviour, mechanical strength, rate of strengthening, and penetrability into fine fractures. The study comprised testing of low-pH cement concretes and grouts with talc and other silicate minerals added for achieving fluidity and high strength. They were composed according to modern packing theories for obtaining low porosity and a minimum amount of cement paste. The use of talc is firstly for decreasing the viscosity of the mixture at casting or injection and secondly for assuring that it can really contribute to the mechanical strength by chemical interaction with the cement component. The need for chemical integrity led to the choice of quartzite as main aggregate in the study. The low-pH cement used was Merit 5000 manufactured by SSAB Merox AB, Oxelösund.For one of the candidate grouts, Portland cement was used in order to get quick hardening, whilst the other contained low-pH cement for providing high strength in the course of time. The principle of composing the aggregate was to obtain a filtering function so that the risk of losing fines is minimized in the construction period when local hydraulic gradients may still be high.It was concluded from this study that theoretical modeling as well as experimental results confirm that concrete mixtures can get high packing degrees and bulk densities if the ballast gradation is suitable and that the role of the fine fraction is thereby very important. The achieved density of the concrete is believed to be sufficiently high in order to make the concrete perform acceptably for very long periods of time even after complete loss of the cement. It was documented that talc serves to reduce the viscosity and contribute to the strength. The relatively low pH of Merit concrete (≈10) in contact with clay indicates that chemically generated destruction of either of the materials will be low. Such concrete, containing properly composed quartz-rich aggregate, and with talc added, fulfills the criteria set for its performance under both normal and high temperature conditions. It was also concluded that grout fluidity is positively affected by the hydrophobic nature of talc and negatively by thixotropic action of other silicates and by early cement hydration. The experiments highlight the role of the rheological properties and the need for proper composition of the grouts. A general conclusion from the grout flow study was that effective injection of grouts into fractures narrower than 100 µm requires that the viscosity is as low as 0.05 Pas and that high injection pressures are used.

  • 2.
    Hatem, Mohammed
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Al-Ansari, Nadhir
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Knutsson, Sven
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Enhancement of Workability of Cement-Poor Concrete by Optimizing Paste Content2014Inngår i: Engineering, ISSN 1947-3931, E-ISSN 1947-394X, Vol. 6, nr 13, s. 869-876, artikkel-id 4Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This study describes the performance of concrete in fresh state, intended for sealing deep boreholes in the host rock of radioactive repositories. Set of different paste volumes, combinations of water-to-powder ratios and fine aggregate contents have been performed within the frame of this study. The main objective was to search for tendencies, logical connections and phenomena that occur for different combination of materials regarding the fluidity and segregation and mainly the effect from the (paste) or fine aggregate content. It shall be pointed out that this investigation is a suggestion on how concrete can be optimized using two simple test methods based on changing the paste content. The results highlighted the importance of having sufficient amounts of filler and cement paste for separate and carry larger particles, which gives the concrete good workability and fluidity at casting. It was concluded that the slump behaviors can be optimized based on the adjustments of the superplastisizer dosage.

  • 3.
    Hatem, Mohammed
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Al-Ansari, Nadhir
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Pusch, Roland
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Knutsson, Sven
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Jonasson, Jan-Erik
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Rheological properties of low pH cement-palygorskite injection grout2013Inngår i: Journal of Advanced Science and Engineering Research, ISSN 2231-8844, Vol. 3, nr 3, s. 167-192Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The rheological properties of cementitious materials containing fine particles, such as mineral admixture were investigated using a Viso Star-L rheometer with cylindrical spindles. Selected features of the behavior of these materials are evaluated from a rheological perspective through literatures results for the past 30 years. One of the important factors that governs the ability of grout to penetrate fractures, channels and porous material is the rheology. The mineral admixture was clay palygorskite which can be used for early gelation because of its thixotropic properties as well as the powder quartz used as aggregate. The cementitious materials were designed and three recipes (MPG1, MPG2 and MPG3) were examined in this research by changing the mix proportions of the mineral admixture palygorskite and water content. For ensuring the accuracy of rheological measurement for the candidate’s grouts, necessary verification was been evaluated such as, influence of mixing time, stability and “time effect” to the accuracy of viscosity measurement, and yield stress as well as the physical properties at 3, 7 and 28 days. The results showed that grouts recipes with quartzite aggregate of different granulometry, are chemically compatible and fulfill the requirement of containing no organic matter. Candidate’s grouts found to satisfy the stable sedimentation criteria with sedimentation rates less than 5% after 2 hours. Furthermore, it was found that the grout recipe 3 followed by 1 showed lower yield stress and plastic viscosity which are (0.1 Pa and 0.269 Pas) and (0.288 Pa and 0.531 Pas) respectively.

  • 4.
    Hatem, Mohammed
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Al-Gburi, Majid
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Al-Ansari, Nadhir
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Jonasson, Jan-Erik
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Pusch, Roland
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Knutsson, Sven
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Design of concrete mixes by systematic steps and ANN2012Inngår i: Journal of Advanced Science and Engineering Research, ISSN 2231-8844, Vol. 2, nr 4, s. 232-251Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The current research caters for the possibility of arriving at a system for designing concrete mixeseasily using available materials locally by specified wide ranges of pre-requisites of three mainprescribed properties to cover a good variety of practical mixes, which are water, water-cement ratioand total aggregate-cement ratio. Using these three properties, a tri-linear form was constructed bygraphical technique manner based on absolute volume approach. This approach defines as asummation of absolute volume for each of these three materials individually water, cement andaggregate should be equal to the absolute volume of whole concrete mixture based on thesealtogether. A quad-form area which includes a wide range of mixes can be formed from thisrepresentation. This area should achieve all the prescribed properties aforementioned. Artificial neuralnetwork concept used in this study also to build easily and quickly system which can be translatedinto Excel sheet. This system predict proportions of concrete mixture and the compressive strengthusing the results designed by the quad-form area method in addition to the data from literature around500 mixes based on local materials used in Iraq. Six input parameters (water to cement ratio, theslump, % of fine to total aggregate content, maximum aggregate size, fineness modulus of fineaggregate and the compressive strength) were used in this system to get the outputs. In addition, nineinput parameters ((water, cement, sand and gravel contents) and the properties of the mix (Finenessmodulus, W/C ratio, the slump, % of fine to total aggregate and the M.A.S)) were used as basis ofcompressive strength model. The algorithm of this system aimed to reduce the high number of trailmixes error as well as saving the labors, cost and time. Results indicated that the concrete mix designand the compressive strength model can be predicted accurately by using graphical perspective andthe ANN approach.

  • 5.
    Hatem, Mohammed
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Emborg, Mats
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Pusch, Roland
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Knutsson, Sven
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Packing theory for natural and crushed aggregate to obtain the best mix of aggregate: research and development2012Inngår i: Proceedings of World Academy of Science, Engineering and Technology, ISSN 2010-376X, E-ISSN 2070-3740, Vol. 67, s. 819-825Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Concrete performance is strongly affected by the particle packing degree since it determines the distribution of the cementitious component and the interaction of mineral particles. By using packing theory designers will be able to select optimal aggregate materials for preparing concrete with low cement content, which is beneficial from the point of cost. Optimum particle packing implies minimizing porosity and thereby reducing the amount of cement paste needed to fill the voids between the aggregate particles, taking also the rheology of the concrete into consideration. For reaching good fluidity superplasticizers are required. The results from pilot tests at Luleå University of Technology (LTU) show various forms of the proposed theoretical models, and the empirical approach taken in the study seems to provide a safer basis for developing new, improved packing models.

  • 6.
    Hatem, Mohammed
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Pusch, Roland
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Al-Ansari, Nadhir
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Knutsson, Sven
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Optimization of concrete by minimizing void volume in aggregate mixture system2012Inngår i: Journal of Advanced Science and Engineering Research, ISSN 2231-8844, Vol. 2, nr 3, s. 208-222Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The behavior of concrete is affected by the size, distribution of the voids, the porosity and of the granulometry of the aggregate mixture. As a consequence it necessary for engineers to consider in detail particle packing concepts and their influence on the physical performance of concrete. The present study included determination of the fineness modulus, cement paste volume based on slump test and the properties of fresh and hardened concrete. It also comprised a study of the applicability of two theoretical models Toufar’s and 4C-packing program for selecting suitable relative amounts of the concrete constituents, for obtaining a minimum void ratio. Comparison of the results was made from using these theoretical models literature-derived experimental data. The models gave similar results and suggest similar combinations of materials to give minimum void ratio. Optimization of the composition of the aggregate material in concrete is beneficial with respect to economy (low cement content), strength and durability. It was noted that minimizing the void ratio (V) tends to raise the stiffness and that the compressive strength (푓푐′) is closely related also to their molding (R) and fineness modules (FM). It was found that the compressive strength can be predicted by applying the formula;푓푐′=−2.1−63.8 푉+0.150 푅+10.4 퐹푀; R2=0.94, and two other relationships related to slump data and cement content.

  • 7.
    Hatem, Mohammed
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Pusch, Roland
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Al-Ansari, Nadhir
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Knutsson, Sven
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Emborg, Mats
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Nilsson, Martin
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Alireza, Pourbakhtiar
    Talc-based concrete for sealing borehole optimized by using particle packing theory2013Inngår i: Journal of Civil Engineering and Architecture, ISSN 1934-7359, E-ISSN 1934-7367, Vol. 7, nr 4, s. 440-455Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The paper describes assessment of the performance of cement-poor concreteson the basis of packing theory. The concretes are intended for sealing segments of deep boreholes and have a small amount of cement for minimizing the mutual chemical impact on the contacting clay seals. The composition is examined by application of packing theory with respect to the cement/aggregate ratio and the gradation of the aggregate material which is crushed quartzite for providing high internal friction after maturation, as well as to talc added for fluidity and to the small amount of cement. Low porosity and micro-structural stability must be guaranteed for very long periods of time. The study exemplifies how packing theory assist designers in selecting optimal proportions of the various components. Optimum particle packing implies minimizing the porosity and thereby reducing the amount of cement paste needed to fill the voids between the aggregate particles. The use of talc as inorganic super-plasticizer since ordinary organic additives for reaching high fluidity at casting are undesirable, and since talc reacts with cement and provides high strength in along-term perspective.

  • 8.
    Hatem, Mohammed
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Pusch, Roland
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Al-Ansari, Nadhir
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Knutsson, Sven
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Jonasson, Jan-Erik
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Emborg, Mats
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Pourbakhtiar, Alireza
    Proportioning of cement-based grout for sealing fractured rock-use of packing models2013Inngår i: Engineering, ISSN 1947-3931, E-ISSN 1947-394X, Vol. 5, nr 10, s. 765-774Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Fractured, very permeable rock hosting repositories for radioactive waste will require grouting. New grout types of possible use where long-term performance is needed should have a small amount of cement for minimizing the increase in porosity that will follow from the ultimate dissolution and erosion of this component. They have to be low-viscous and gain strength early after injection and packing theory can assist designers in selecting suitable proportions of various grout components. Optimum particle packing means that the porosity is at minimum and that the amount of cement paste needed to fill the voids between aggregate particles is very small. Low porosity and microstructural stability must be guaranteed for long periods of time. Organic additives for reaching high fluidity cannot be used since they can give off colloids that carry released radionuclides and talc can be an alternative superplasticizer. Low-pH cement reacts with talc to give high strength with time while Portland cement gives early but limited strengthening. The clay mineral palygorskite can be used for early gelation because of its thixotropic properties. Once forced into the rock fractures or channels in soil it stiffens and serves as a filter that prevents fine particles to migrate through it be lost. However, its hydrophilic potential is too high to give the grout a high density and high strength. According to the experiments carried out most of the investigated grouts are injectable in fractures with apertures down to 100 μm.

  • 9.
    Hatem, Mohammed
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Pusch, Roland
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Knutsson, Sven
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Study of cement-grout penetration into fractures under static and oscillatory conditions2015Inngår i: Tunnelling and Underground Space Technology, ISSN 0886-7798, E-ISSN 1878-4364, Vol. 45, s. 10-19Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Grouting of the rock surrounding high-level waste (HLW) can serve to minimize groundwater flow around it and thereby to retard erosion of waste-embedding clay (buffer) and transport of possibly released radionuclides. Earlier attempts have shown the efficiency of superimposing the injection pressure with oscillations for bringing cement-rich grouts into narrow fractures using organic superplasticizers. However, these are short-lived and can produce radionuclide-bearing organic colloids, and should be replaced by inorganic agents. Portland cement in grouts is not long lived and low-pH cements are preferable as is also reduction of the cement content to an absolute minimum. The present study describes the composition and performance of candidate grouts in laboratory experiments with injection into plane-parallel slots with different aperture. The study included development of a simple and quick method for estimating the viscosity on the construction site for adapting the grout recipe to the injectability of the rock. A simple theoretical model for predicting grout penetration gives fair agreement with laboratory data. The longevity of the grout under various conditions is believed to be sufficient for use in HLW repositories implying waste placement in very deep holes

  • 10.
    Hatem, Mohammed
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Pusch, Roland
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Knutsson, Sven
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Hellström, J. Gunnar I.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Rheological Properties of Cement-Based Grouts Determined by Different Techniques2014Inngår i: Engineering, ISSN 1947-3931, E-ISSN 1947-394X, Vol. 6, nr 5, s. 217-229Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The rheological properties of cement-based grouts containing talc or palygorskite were investigated for optimizing fluidity and quick strengthening at injection. The fluidity controls the ability of grout to penetrate fractures and can be determined by pipe flow tests, Marsh funnel tests, mini-slump cone tests and rheometer tests. The grouts were 1) Talc for fluidity and strength by reacting with cement, 2) Palygorskite (attapulgite) for early gelation by being thixotropic, and 3) Powdered quartz for chemical integrity. The freshly prepared grouts behaved as Bingham fluids with viscosities from 0.151 to 0.464 Pas and yield stresses 5.2 Pa to 36.7 Pa. Statistical analysis of the flow test data converted Marsh flow time into viscosity. The pipe flow tests gave 26.5% higher values than the viscometer for grout with Portland cement and talc, and about 13.7% lower than the viscometer data for the grout with low-pH cement and talc. The big Marsh funnel gave valuesdiffering by 5.2% - 5.3% from those of the viscometer for grout with talc and Portland, and Merit 5000 cements. For grout with palygorskite the viscosity was at least twice that of the other grouts. Grout fluidity was positively affected by talc and negatively by palygorskite and early cement hydration

  • 11.
    Hatem, Mohammed
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Pusch, Roland
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Knutsson, Sven
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Jonasson, Jan-Erik
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Performance of Cement-poor Concrete with Different Superplasticizers2014Inngår i: International Journal of Research and Reviews in Applied Sciences, ISSN 2076-734X, E-ISSN 2076-7366, Vol. 18, nr 2, s. 163-172Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Concrete can be used for casting plugs in deep boreholes where fracture zones are intersected. They will be exposed to flowing groundwater and be in contact with very tight seals of smectite clay installed where the surrounding rock is tight. The cast concrete must be able to carry the clay segments placed over it after a few days. Its bearing capacity does not have to be very high after that since the clay soon adheres to the rock and carries itself. The concrete must be poor in cement for minimizing the risk of creation of voids caused by dissolution of the cement and it should have “inert” aggregate of quartz-rich material. Inorganic superplasticizers instead of conventional organic ones should be used for eliminating the risk of degradation and loss by formation of colloids that can carry radionuclides to the biosphere from holes bored in repository rock. The two concrete types discussed in the present study had Portland and Merit 5000 low pH cement as binders and crushed quartzite as aggregate. Talc mineral powder and ordinary organic Glenium 51 were used as superplasticizers for comparing their impact on the physical properties. The matrix of the cement-poor talc concrete gave ductile behaviour during initial hardening. The very dense matrix of either of the concretes would not lead to compression of the system even after complete loss of cement, which will happen over a longer period of time. The overall conclusion was that talc as superplasticizer and conditioner of the concrete can make the concrete sufficiently fluid for constructing seals at depth in boreholes, and react with cement to provide high strength with some delay. pH is much lower in Merit than in Portland concrete, which causes less impact on the clay seals. Portland concrete has five times higher strength than Merit concrete after a week but three times lower strength after 28 days.

  • 12. Hatem, Mohammed
    et al.
    Pusch, Roland
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Knutsson, Sven
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Warr, Laurence
    Greifswald University, Geographical & Geological Department, Germany.
    Hydrothermal alteration of clay and low pH concrete applicable to deep borehole disposal of high-level radioactive waste: A pilot study2016Inngår i: Construction and Building Materials, ISSN 0950-0618, E-ISSN 1879-0526, Vol. 104, s. 1-8Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In the very deep borehole (VDH) concept for high level radioactive waste disposal, the combined usage of clay and concrete provides an attractive way of achieving both high strength and low permeability required for sealing the various sections of the hole. The concrete is required for mechanical stability where water-bearing fracture zones are intersected, whereas the clay effectively seals sections in stable rock masses. As both the clay and concrete may be exposed to temperatures in the range of 60–150 °C in various parts of the hole, there is a need to address the stability of these materials under thermally enhanced aqueous conditions. In this pilot study, a new type of organic-free, low pH concrete based on granulated blast furnace slag is tested, which is hardened and altered under hydrothermal conditions in the laboratory. The results presented show that both adequate compressive strength (up to ∼9 MPa) and low hydraulic conductivity (down to ∼5.6 × 10−10) is attained at elevated temperatures ranging up to 150 °C, indicating that clay-concrete sealing can be a successful method used to prevent radionuclides from migrating vertically up through the borehole repository.

  • 13.
    Hatem, Mohammed
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Pusch, Roland
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Warr, Laurence
    Institute of Geography and Geology, Ernst-Moritz-Arndt-University of Greifswald.
    Kasbohm, Jörn
    Institute of Geography and Geology, Ernst-Moritz-Arndt-University of Greifswald.
    Knutsson, Sven
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Interaction of clay and concrete relevant to the deep disposal of high-level radioactive waste2015Inngår i: Applied Clay Science, ISSN 0169-1317, E-ISSN 1872-9053, Vol. 118, s. 178-187Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A concept for the disposal of highly radioactive waste at depth in the Earth’s crust using very deep bore-holes requires that the upper 2 km’s of the 800 mm diameter, steeply drilled holes, be effectively sealed. This can be achieved by using dense smectitic clay where the rock is weakly fractured and strengthening with concrete when fracture zones are encountered. Earlier investigations have shown that chemical reactions between the clay and concrete can be expected both in the upper part where the temperature is lower than 90oC and in the deeper section where the temperature reaches up to 150oC. To study further this interaction, hydrothermal experiments were conducted using mixed-layer (illite/smectite) Holmehus clay and a low pH slag-based concrete placed in contact under isothermal conditions at 21°C, 100oC and 150oC for a period of 8 weeks. The sample sets, which consisted of two clay discs separated by concrete cast on the lower clay disc, were extracted in undisturbed form and exposed to uniaxial pressure for measuring the compressive strength at successively increasing pressures. Compression tests underenhanced thermal conditions led to strengthening of both the clay and concrete. X-ray diffraction and electron microscopy analysis of the material revealed an increasing degree of cation exchange at higher temperatures with the cement, whereby Ca replaced Na in the interlayer sites of smectite layers. Dissolution of illite/smectite was also evident occurring at enhanced temperatures, with a decrease in K, Mg and Fe content with advanced alteration. The enhanced strength of clay can be partly attributed to the precipitation of cement phases from circulating fluids, including precipitation of gypsum.

  • 14.
    Pusch, Roland
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Hatem, Mohammed
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Kasbohm, Jörn
    Greifswald University.
    Knutsson, Sven
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Roles of clay and concrete in isolating high-level radioactive waste in very long holes2013Inngår i: International Journal of Research and Reviews in Applied Sciences, ISSN 2076-734X, E-ISSN 2076-7366, Vol. 16, nr 2, s. 263-273Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Groundwater flow transports possibly released radionuclides from underground repositories to the biosphere. It can also make construction difficult as is obvious from examining technical solutions for disposal of high-level radioactive waste (HLW) in long subhorizontally bored holes (KBS-3H) and in very deep boreholes (VDH). The presence of intersected, water-bearing fracture zones requires concrete for sealing these parts of the holes while the rest contains canisters surrounded and separated by dense, expandable clay. Casting of the concrete should be preceded by grouting of the fractured rock using cementitious materials composed so that mutual physical and chemical interaction do not degrade either of them. For the sake of rock stability the horizontal holes have to be located at very moderate depth, 400-500 m, where the rock has a high average hydraulic conductivity, while the slimmer, steep holes reaching down to 4 km are kept stable by using clay mud in the construction phase and dense clay for long term performance. The rock at this depth is much less permeable than higher up and the groundwater sufficiently salt to be maintained there, causing only local thermally induced circulation of possibly contaminated water. The KBS-3H concept involves practical difficulties and risks in the installation of the clay seals and waste canisters, for which the risk of shearing by slip of frequently intersected steep fractures is a major threat after closure of the repository. The VDH concept relies on effective sealing of the upper part of the deep holes and puts less demand on the seals in the lower, waste-bearing part, for which the buoyancy conditions of the groundwater make it a major barrier to upward migration of possibly released radionuclides.

  • 15.
    Pusch, Roland
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Hatem, Mohammed
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Knutsson, Sven
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    VDH – a case of ostrich philosophy or a serious alternative for the disposal of highly radioactive waste?2014Inngår i: Waste Management and the Environment VII / [ed] C.A. Brebbia; G. Passerini; H. Itoh, Southampton: WIT Press, 2014, s. 377-390Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Two basically different concepts for disposal of highly radioactive waste are the often cited KBS-3 method implying isolation of such waste in copper canisters in short holes bored from tunnels at a depth of a few hundred meters, and disposal in the lower part of 4 km deep holes (VDH). The deep hole concept has the advantage that the waste packages will be located in very salt, stagnant groundwater in rock that is much less permeable than shallow rock with repositories of KBS-3V type. Disadvantages are that some of the techniques for installation have not yet been demonstrated and that retrieval of damaged or stuck canisters is deemed more difficult than for KBS-3V. Both concepts require precise adaption of canister and seal positions to the rock structure, which, for KBS-3 repositories, is not known until the tunnels have been constructed. For VDH, pilot borings provide such knowledge at low cost at a very early stage. The deep holes need to be supported by casings and all work deeper than 500 m must be made with clay mud in them. Reconsideration of the design and function of VDH shows that it has significant advantages, primarily respecting cost and construction time, and that new types of concrete for sealing purposes can make such repositories safer than KBS-3V disposal since seismic and tectonic events are less detrimental and future glaciations will cause much less disturbance. The most important value is that the groundwater that can possibly become contaminated by failing engineered barriers will stay at more than 2000 m depth and that there is no mechanism that can bring it up to the biosphere

  • 16.
    Pusch, Roland
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Knutsson, Sven
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Al-Taie, Laith
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Hatem, Mohammed
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Optimal ways of disposal of highly radioactive waste2012Inngår i: Natural Science, ISSN 2150-4091, E-ISSN 2150-4105, Vol. 4, nr 11A, s. 906-918Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Multibarrier concepts are commonly proposed for effective isolation of highly radioactive waste (HLW). Present concepts consider the host rock as a barrier by retarding migration of possibly released radionuclides to the biosphere, containers for preventing release of radionuclides, and “buffer clay” embedding the canisters for providing ductility and minimizing the risk of container breakage and for delaying migration of possibly escaping radionuclides. Closer analysis of the isolating functions shows that rock will only serve as a mechanical protection of the “nearfield”, the containers of proposed types can be short-lived, and the surrounding clay will be increasingly permeable and stiffen hence becoming less ductile with time. A different approach, representing an alternative to the common concepts, can be safer and cheaper. It takes the HIPOW copper canister as the only major barrier and a cheap but sufficiently efficient buffer as embedment. The repository can consist of an abandoned copper mine, an option being to place HLW in emptied drifts while mining is still going in not yet exploited parts of the ore body.

  • 17.
    Pusch, Roland
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Knutsson, Sven
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Hatem, Mohammed
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Isolation of hazardous waste in crystalline rock2012Inngår i: Journal of Earth Sciences and Geotechnical Engineering, ISSN 1792-9040, E-ISSN 1792-9660, Vol. 2, nr 3, s. 57-75Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Radioactive waste from the nuclear industry and hazardous products from chemical industries need to be effectively isolated from the biosphere for a very long time. Highly radioactive waste gives off heat and requires disposal at depth in special repositories while low-level radioactive waste, pesticides and mercury and arsenic, can be stored in deep mines. The multiple barrier principle implies that the rock and engineered barriers combine to provide isolation but assessment of the constitution and performance of crystalline rock reduces its role to provide “mechanical support” to waste containers rather than true isolation of them. Smectitic clay is required for achieving this but its isolating capacity is limited over time, and long-lasting waste containers are needed as well. The waste isolation effect of clay and containers can allow for constructing repositories in rock of rather poor quality, represented by abandoned mines, and waste containers of 100 % copper further reduce the need for very well planned and constructed repositories.

  • 18.
    Pusch, Roland
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Knutsson, Sven
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Ramqvist, Gunnar
    El-Tekno AB.
    Hatem, Mohammed
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Pourbakhtiar, Alireza
    Can sealing of rock hosting a repository for highly radioactive waste be relied on?2012Inngår i: Natural Science, ISSN 2150-4091, E-ISSN 2150-4105, Vol. 4, nr 11A, s. 895-905Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Multibarrier systems are commonly proposed for effective isolation of highly radioactive waste (HLW). Presently considered concepts take the host rock as a barrier claiming it to retard migration of possibly released radionuclides from HLW containers to the biosphere. This capacity is small unless water-bearing fracture zones intersecting the blasted waste-containing tunnels and excavation-disturbance zones around them can be sealed by grouting and construction of bulkheads, but this is effective only for a very limited period of time as explained in the paper. The disturbed zones thence make the entire repository serve as a continuous hydraulic conductor causing quick transport of released radionuclides up to the biosphere. The dilemma can be solved by accepting the short-circuiting function of the disturbed zones along the tunnels on the condition that totally tight waste containers be used. Deep holes bored in the site selection phase through the forthcoming repository can be effective pathways for radionuclides unless they are properly sealed. They are small-scale equivalents of tunnels but do not have any ex-cavation damage and can be effectively sealed by using clay and concrete of new types. Applying this principle to very deep boreholes with a diameter of a few decimeters would make it possible to safely store slim, tight HLW canisters for any period of time.

  • 19.
    Pusch, Roland
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Ramqvist, Gunnar
    D ElTekno AB.
    Kasbohm, Jörn
    GeoENcon Ltd.
    Knutsson, Sven
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Hatem, Mohammed
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    The concept of highly radioactive waste (HLW) disposal in very deep boreholes in a new perspective2012Inngår i: Journal of Earth Sciences and Geotechnical Engineering, ISSN 1792-9040, E-ISSN 1792-9660, Vol. 2, nr 3, s. 1-24Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Two basically different concepts for disposal of highly radioactive waste are the often cited KBS-3 method and a concept termed VDH (Very Deep Boreholes). So far, the deep hole concept has been ranked as number two because the canisters are not assumed to be retrievable and because some of the techniques for installation of the waste are not yet at hand. Reconsideration of the design and function of VDH shows that, in addition to the advantage of no transport of released radionuclides by groundwater flow up to the ground level because of the almost stagnant salt groundwater at depth, the rock at depth is considerably less permeable than for mined repositories at shallow depth. A further advantage is that VDH will be less affected by future glaciations. Less good is that precise adaption of canister and seal positions to the rock structure cannot be made until boring of the deep holes is complete. Furthermore, the deep holes need to be supported by casings and all work deeper than 500 m must be made with mud in them. Retrieval of damaged casings and stuck canisters may be more difficult than in mined repositories.

  • 20.
    Pusch, Roland
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Ramqvist, Gunnar
    Eltekno AB, Oscarshamn, Sweden.
    Knutsson, Sven
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Hatem, Mohammed
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Medium-deep or very deep disposal of highly radioactive waste?2013Inngår i: Journal of Civil Engineering and Architecture, ISSN 1934-7359, E-ISSN 1934-7367, Vol. 7, nr 12, s. 1548-1565Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Several of the commonly proposed concepts for disposal of highly radioactive waste (HLW) imply construction at medium depth (400-600 m) in granitic rock, which is excellent for constructing a stable repository since it provides effective mechanical protection of the waste. A drawback is that major water-bearing fracture zones are frequent and must be avoided in the site selection process since they can undergo large deformations caused by seismic and tectonic events and cause failure of waste containers located in or near them. The effect of such events can be minimized by surrounding them with ductile “buffer” clay that retards groundwater-driven adflow. An alternative concept is placement of HLW in very deep boreholes (VDH) where the rock is much less permeable and where the very salt, heavy groundwater is stagnant. The boreholes are proposed to be 4 km deep and grouped in a small number of sites. The upper 2 km parts, with temperatures lower than about 100oC, are sealed by being filled with perforated supercontainers with dense clay blocks, while the lower part contains supercontainers with waste canisters and dense clay blocks, raising the temperature between 2 and 4 km to 100-150oC. The holes are kept filled with clay mud into which the supercontainers are inserted where the rock contains few fractures, while concrete is cast where the rock is fracture-rich. In the upper part clay migrates through the perforated supercontainers and consolidates the mud. In the lower part clay the same process takes place where the clay block in each supercontainer is located, while the rest of the mud retains its original low density but undergoes stiffening. In the upper, sealed part of the hole, the consolidated clay will be much tighter than the surrounding rock, while in the lower part the mud will be more permeable but still capable of limiting water circulation within the hole. The paper compares the two repository principles and recommends closer examination of the very deep hole concept, which has obvious advantages respecting both performance and cost.

  • 21.
    Pusch, Roland
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Warr, Laurence
    Greifswald University, Geographical & Geological Department, Germany.
    Grathoff, Georg
    Greifswald University, Geographical & Geological Department, Germany.
    Pourbakhtiar, Alireza
    Knutsson, Sven
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Hatem, Mohammed
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    A talc-based cement-poor concrete for sealing boreholes in rock2013Inngår i: Engineering, ISSN 1947-3931, E-ISSN 1947-394X, Vol. 5, nr 3, s. 251-267Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Deep investigation boreholes in crystalline rock for site selection of repositories for high-level radioactive waste are proposed to be sealed by installing a series of dense concrete and clay plugs. These should prevent radionuclides from leaking canisters at depth to migrate to the biosphere through the holes. The concrete seals will be installed where the holes intersect water-bearing fracture zones to serve as stable and low-permeable supports for adjacent clay plugs. Low porosity and microstructural stability must be guaranteed for many thousands of years and ordinary Portland cement with organic superplastizer will not fulfil the requirements since the high pH will cause degradation of contacting clay and the organic additive can produce colloids with a capacity to carry radionuclides up to the biosphere. Very cement-poor concrete (<8 %) based on low-pH cement and with talc as plasticizer is an option but it matures more slowly, which requires that the construction of seals is made so that sufficient bearing capacity for carrying overlying clay seals is reached.

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